Members of the cytochrome P450 superfamily of enzymes catalyze the oxidative metabolism of a variety of substrates, including natural compounds such as steroids, fatty acids, prostaglandins, leukotrienes, and vitamins, as well as drugs, carcinogens, mutagens, and xenobiotics. Cytochrome P450s, also known as P450 heme-thiolate proteins, usually act as terminal oxidases in multi-component electron transfer chains, called P450-containing monooxygenase systems. Specific reactions catalyzed include hydroxylation, epoxidation, N-oxidation, sulfooxidation, N-, S-, and O-dealkylations, desulfation, deamination, and reduction of azo, nitro, and N-oxide groups. These reactions are involved in steroidogenesis of glucocorticoids, cortisols, estrogens, and androgens in animals; insecticide resistance in insects; herbicide resistance and flower coloring in plants; and environmental bioremediation by microorganisms. Cytochrome P450 actions on drugs, carcinogens, mutagens, and xenobiotics can result in detoxification or in conversion of the substance to a more toxic product. Cytochrome P450s are abundant in the liver, but also occur in other tissues. (See ExPASY ENZYME EC 1.14.14.1; Prosite PDOC00081 Cytochrome P450 cysteine heme-iron ligand signature; PRINTS EP450I E-Class P450 Group I signature; and Graham-Lorence, S. and Peterson, J. A. (1996) FASEB J. 10:206-214.)
Four hundred cytochrome P450s have been identified in diverse organisms including bacteria, fungi, plants, and animals (Graham-Lorence, supra). The B-class is found in prokaryotes and fungi, while the E-class is found is found in bacteria, plants, insects, vertebrates, and mammals. Five subclasses or groups are found within the larger family of E-class cytochrome P450s (PRINTS EP450I E-Class P450 Group I signature).
All cytochrome P450s use a heme cofactor and share structural attributes. Most cytochrome P450s are 400 to 530 amino acids in length. The secondary structure of the enzyme is about 70% alpha-helical and about 22% beta-sheet. The region around the heme-binding site in the C-terminal part of the protein is conserved among cytochrome P450s. A ten amino acid signature sequence in this hemeiron ligand region has been identified which includes a conserved cysteine involved in binding the heme iron in the fifth coordination site. In eukaryotic cytochrome P450s, a membrane-spanning region is usually found in the first 15-20 amino acids of the protein, generally consisting of approximately 15 hydrophobic residues followed by a positively charged residue. (See Prosite PDOC0081, supra; Graham-Lorence, supra.)
Cytochrome P450 enzymes are involved in cell proliferation and development. The enzymes have roles in chemical mutagenesis and carcinogenesis by metabolizing chemicals to reactive intermediates that form adducts with DNA (Nebert, D. W. and Gonzalez, F. J. (1987) Ann. Rev. Biochem. 56:945-993). These adducts can cause nucleotide changes and DNA rearrangements that lead to oncogenesis. Cytochrome P450 expression in liver and other tissues is induced by xenobiotics such as polycyclic aromatic hydrocarbons, peroxisomal proliferators, phenobarbital, and the glucocorticoid dexamethasone (Dogra, S. C. et al. (1998) Clin. Exp. Pharmacol. Physiol. 25:1-9). A cytochrome P450 protein may participate in eye development as mutations in the P450 gene CYP1B1 cause primary congenital glaucoma (Online Mendelian Inheritance in Man (OMIM) *601771 Cytochrome P450, subfamily I (dioxin-inducible), polypeptide 1; CYP1B1). Cytochrome P450s are also involved in drug interactions, because the induction of a cytochrome P450 by one drug may affect the metabolism of another drug by the enzyme (Katzung, B. G. (1995) Basic and Clinical Pharmacoloy, Appleton & Lange, Norwalk Conn., pp. 48-59).
Cytochrome P450s are associated with inflammation and infection. Hepatic cytochrome P450 activities are profoundly affected by various infections and inflammatory stimuli, some of which are suppressed and some induced (Morgan, E. T. (1997) Drug Metab. Rev. 29:1129-1188). Effects observed in vivo can be mimicked by proinflammatory cytokines and interferons. Autoantibodies to two cytochrome P450 proteins were found in patients with autoimmune polyenodocrinopathy-candidiasis-ectodermal dystrophy (APECED), a polyglandular autoimmune syndrome (OMIM *240300 Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy).
Mutations in cytochrome P450s have been linked to metabolic disorders, including congenital adrenal hyperplasia, the most common adrenal disorder of infancy and childhood; pseudovitamin D-deficiency rickets; cerebrotendinous xanthomatosis, a lipid storage disease characterized by progressive neurologic dysfunction, premature atherosclerosis, and cataracts; and an inherited resistance to the anticoagulant drugs coumarin and warfarin (Isselbacher, K. J. et al. (1994) Harrison's Principles of Internal Medicine, McGraw-Hill, Inc. New York, N.Y., pp. 1968-1970; Takeyama, K. et al. (1997) Science 277:1827-1830; Kitanaka, S. et al. (1998) N. Engl. J. Med. 338:653-661; OMIM *213700 Cerebrotendinous xanthomatosis; and OMIM #122700 Coumarin resistance). Extremely high levels of expression of the cytochrome P450 protein aromatase were found in a fibrolamellar hepatocellular carcinoma from a boy with severe gynecomastia (feminization) (Agarwal, V. R. (1998) J. Clin. Endocrinol. Metab. 83:1797-1800).
The discovery of a new human cytochrome P450 and the polynucleotides encoding it satisfies a need in the art by providing new compositions which are useful in the diagnosis, prevention, and treatment of cell proliferative, developmental, autoimmune/inflammatory, and metabolic disorders.